Room temperature curing compositions based on oxyalkylene polymers containing reactive silicon groups can be used, for example, as sealants for construction (commonly referred to as “modified silicone sealants”), and have high performance. Among various characteristics required for such curing compositions, mechanical properties, such as modulus, elongation at break, and strength at break, along with long-lasting weatherability are important. Various studies have been conducted on these properties. As a result, with respect to mechanical properties, such as modulus, elongation at break, and strength at break, it is known that by adding a phthalate ester, a polyether plasticizer, or the like to a curable composition, physical properties suitable for sealants can be obtained. With respect to weatherability, each of Japanese Unexamined Patent Application Publication Nos. 59-122541, 60-031556, 63-112642, 6-172631, 7-90171, etc., discloses that by blending a reactive silicon group-containing vinyl polymer with a reactive silicon group-containing oxyalkylene polymer, the weatherability can be improved compared with when the reactive silicon group-containing oxyalkylene polymer is used alone.
Ceramic siding boards are inexpensive, fire-resistant construction materials used for walls or the like which are produced by compounding main raw materials, such as cement, fly ash, or perlite, with organic fibers, etc., followed by hardening. When siding boards are constructed, since gaps (joints) occur between the siding boards, waterproof and airproof treatment is performed using sealants. With the recent prolongation of performance guarantee time for buildings, such as houses, sealants are also required not to deteriorate with time. Sealants in general, including sealants for construction, are required to have high elongation at break. In particular, with respect to sealants for ceramic siding boards in which large shrinkages occur with time, high elongation at break is required.
For example, according to the test method for sealants for ceramic siding established by Japan Fiber Reinforced Cement Siding Manufacturers Association, an elongation at break of 250% or more is required. However, in expectation of deterioration with time, desirably, the elongation at break is twice as large as this value, i.e., 500% or more, and preferably 600% or more. Furthermore, since sealants for siding boards are directly exposed to outdoor environment, weatherability is required.
With respect to a cured object obtained from a composition containing a reactive silicon group-containing oxyalkylene polymer and a reactive silicon group-containing vinyl polymer, it has been found that although excellent weatherability is exhibited, elongation at break is lower than that of a cured object obtained from a composition which does not contain a reactive silicon group-containing vinyl polymer. In particular, as the sealant used for joints of ceramic siding boards, the elongation at break is insufficient. When a composition which contains a reactive silicon group-containing oxyalkylene polymer and a reactive silicon group-containing vinyl polymer and which produces a cured object with low elongation at break is used, in order to obtain sufficient elongation at break, a large amount of plasticizer must be used, and thus compounding is restricted, which is disadvantageous. Consequently, it is necessary to modify the reactive silicon group-containing oxyalkylene polymer and/or the reactive silicon group-containing vinyl polymer so that the resultant cured object has excellent elongation properties.
Furthermore, as described in “Kenchikuyo sealants (Sealants for construction)” (published by Japan Sealant Industry Association), at page 158, phthalate ester plasticizers having high plasticizing effect are often used for reactive silicon group-containing oxyalkylene polymers. Recently, in view of environmental concerns, use of plasticizers other than phthalate ester plasticizers is required in some cases. However, even if a polymer which produces a cured object with excellent elongation properties is obtained, if the plasticizing efficiency of the plasticizer is low, the improvement effect of the polymer is cancelled out.
Furthermore, it is generally known that if the molecular weight of the polymer in the composition, in particular, the molecular weight between crosslinking points (molecular weight of the chain between reactive silicon groups), increases, elongation properties improve. However, if the molecular weight of the polymer increases, the viscosity of the polymer increases, which in turn increases the viscosity of the composition, and workability decreases when the composition is used as the sealant. In particular, when a high molecular weight plasticizer, such as polypropylene glycol (PPG), is used, the viscosity of the composition increases compared with the use of a low molecular weight plasticizer, such as di(2-ethylhexyl) phthalate (DOP) or diisodecyl phthalate (DIDP).